Spring has been warmer and has arrived earlier in the last 30 to 50 years.

There are a number of ways of trying to figure out when spring arrives. One measure is when the snow starts to melt. Another is precipitation; studies have found that across most of the Northwest over to New England, more rain falls now than snow. Other studies show there’s less snow on the ground on April 1 now than there was in the 1950s. Most rivers rise earlier, and some plants have been greening earlier. By all these measures, we can say that spring is coming earlier.

There are few places where we could explain even half of the hastening of spring by natural forces alone. We’ve seen warmer springs and earlier onset over the last 30 to 50 years, which makes sense, because in that time we’ve dumped a lot more greenhouse gases into the atmosphere than we did in the early 1900s. Whether these trends accelerate or just keep eroding away at when spring arrives will depend on how much people reduce greenhouse gas emissions. Temperatures will rise and the arrival of spring will keep getting earlier pretty much in proportion to the amount of greenhouse gases going into the atmosphere.

Story as told to Sarah Parsons. This article originally appeared in Plenty in February 2008.